116-2 Constraining the structure and evolution of regolith on the lunar mare basalts

Session: Lunar Science and Exploration in the Artemis Era (Posters)

Poster Booth No.: 323

Presenting Author:

Cole Nypaver

Authors:

Nypaver, Cole¹, Morgan, Gareth²

(1) Smithsonian Institution, Washington, DC, USA, (2) Planetary Science Institute, Washington, AZ, USA,

Abstract:

Since their emplacement via predominantly effusive-style volcanic eruptions, the lunar maria basalts have been subjected to continual meteoroid bombardment. Consequently, a regolith layer of unconsolidated material has accumulated and evolved on the lunar mare deposits since their initial formation and solidification. This canonical view of lunar mare regolith evolution dictates that older mare basalts should have undergone enhanced mechanical breakdown and regolith accumulation due to their extended exposure to impact gardening processes. Recent work, however, challenges this ubiquitous view of regolith formation, suggesting that the characteristics of the volcanic protolith (parent rock) plays a significant role in subsequent regolith development. Here we use derived data from the LRO Mini-RF (12.6 cm - δCPR) and Diviner (SAM RA) instruments to constrain the geologic controls on lunar regolith structure for the near side mare basalts. Specifically, we use δCPR (sensitive to cm-scale surface and subsurface rocks) and SAM RA (sensitive to m-scale surface rocks) data to further define any variability in the subsurface dimension of mare regolith structure and rock contents. Our results indicate that units within Mare Humorum, Mare Frigoris, and Mare Humorum stand out as outliers in the derived SAM RA and δCPR/age relationships. These results agree with the findings of prior work showing anomalously elevated Diviner RA values in different regions of Mare Frigoris, Mare Humorum, and Mare Procellarum. Regional agreement between the δCPR and SAM RA residuals suggest that cm/decimeter scale subsurface rock populations correlate in some instances with the meter-scale surface rock populations observed in past work. Thus, the depth distribution of ~> 10 cm rock fragments appears to be consistent throughout the upper lunar regolith in some regions where the δCPR and RA residuals show good agreement. However, there are several regions — such as Mare Frigoris and Mare Imbrium — where the δCPR and SAM RA residuals do not correlate well. For example, most Mare Frigoris units stand out as positive residuals in δCPR data, but less so in SAM RA data. Such deviations indicate a disconnect between surface and subsurface rock populations that may be caused by an increased rate of regolith overturn or rock production rate in some areas of the nearside lunar maria.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4720

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